Is plate tectonics occurring today?

In this brief article, I focus on the question of whether or not the primary
plate tectonic processes of seafloor spreading and subduction are occurring
in the present day. Restricting the scope to the present moment eliminates
many of the issues arising from uniformitarian bias on the part of the secular
earth science community. I discuss the GPS determinations of present-day plate
motions, the present-day distribution of seismicity, the topography and elevated
heat flow along the present-day mid-ocean ridge system, the slip and fault
plane orientation of present-day mega-earthquakes, and the close association
of most present-day volcanism with deep ocean trenches. I conclude that these
multiple, largely independent, lines of observational evidence strongly support
the premise that coherent plate motions, commonly on the order of centimetres
per year, are occurring and that seafloor spreading and subduction are close
to undeniable realities.

GPS testifies to the reality that plates are currently moving

Data courtesy of NASAFigure 1. Time history of location of the Cook Islands station
in the western Pacific as determined by GPS over the interval 2002–2011.

I frame my discussion of these topics around several claims Michael Oard made
in his response1 to my letter2 in
J. Creation 25(2), where I outlined my reasons for concluding
that rapid cooling of the ocean lithosphere was responsible for the rapid sea
level drop in the later portion of the Flood.

In his response to my letter, Oard claimed that present-day GPS measurements,
which I had offered as definitive evidence that plate tectonics is occurring
today, admit “other, non-PT, explanations”. Yet he provides no
hint as to what those other explanations might be. In this context it seems
useful to summarize the present status of GPS determinations of plate motions.
Currently, the Jet Propulsion Laboratory, under contract with NASA, collects
and compiles precise geodetic position measurements of each of over 2,000 GPS
receiver stations distributed worldwide, utilizing a constellation of 30 GPS
satellites. Figure 1 displays the relative latitude and longitude measured
from 2002 to 2011 as a function of time for the Cook Islands GPS station in
the western Pacific. Lines fit through these points over that time interval
give an average northward velocity for that station of 3.5 cm/yr and an average
westward velocity of 6.3 cm/yr relative to the GPS reference frame for the
earth. Because the noise in these data is so small, the confidence level in
the velocity implied by the change in the station position with time is high.

Photo courtesy of NASAFigure 2. Displacement rates of GPS stations in the western
Pacific region as compiled by JPL.

The time history data for each of these more than 2,000 stations is available
on the JPL website, sideshow.jpl.nasa.gov/mbh/series.html, together with an
interactive global map that summarizes these data in a visual way. Figure 2
is a portion of this map that displays the western Pacific, south-eastern Asia,
and Australia. These GPS measurements show that the Pacific Plate is currently
moving coherently to the west-northwest relative to the trenches on its western
margin at a rate of about 7.5 cm/ yr. They show that India is moving as a coherent
block to the northeast relative to the region to the north. They show that
Australia is moving north-northeastward as a coherent block toward the ocean
trenches to its north.

Elsewhere these data show that sites west of the San Andreas Fault are moving
north-westward relative to sites to the east of the fault by several cm/yr.
They also document that Easter Island on the Nazca Plate in the south-eastern
Pacific is currently moving eastward at about 7 cm/yr. This implies seafloor
spreading is occurring across the East Pacific Rise to the west of Easter Island
at a rate of about 14 cm/yr.

These data document the reality of the defining
aspects of plate tectonics in operation in our world today. It is hard for me
to imagine an alternative explanation.

These measurements demonstrate, with little room for debate, that plates are
real entities and that they are currently in motion across the face of the
earth. The measurements document the reality of plate divergence, or spreading,
across the mid-ocean ridge system. With equal clarity they document the reality
of plate convergence, i.e. subduction, at deep ocean trenches. They also document
the reality of transform faults, such as the San Andreas, along certain portions
of plate boundaries. In other words, these data document the reality of the
defining aspects of plate tectonics in operation in our world today. It is
hard for me to imagine an alternative explanation. Nevertheless, I am eager
to learn about the ones Oard mentioned but did not describe.

Oard makes the further claim that the inclined zones of intense seismicity
adjacent to the deep ocean trenches, known as Wadati-Benioff zones, likewise
admit “other, non-PT, explanations”. Again, he provides no clue
as to what those other explanations might be. Like the GPS measurements, the
distribution and character of earthquakes that occur on a daily basis across
the world testify powerfully to the present reality of plate motion. Figure
3 shows the distribution of earthquakes of greater than 4.5 magnitude for the
period 1991–1996 as compiled by the U.S. Geological Survey. These earthquakes
display a strong correlation with plate boundaries. Furthermore, the deep events
are associated exclusively with the zones of plate convergence.

Data courtesy of NASAFigure 3. Global distribution of earthquakes with magnitudes
greater than 4.5 during years 1991–1996, as compiled by the U.S. Geological
Survey.

Earthquakes represent an important diagnostic of zones of deformation in the
lithosphere. For an earthquake to occur, the rock must be cool enough to deform
in an elastic manner. In general this means that to support earthquakes, rock
temperature must lie below the brittle– ductile transition temperature,
which, for granitic crust, is about 300°C and for olivine-rich ocean lithosphere
is about 600°C.3,4 Below
this transition temperature, rock behaves elastically and stores elastic energy
as it is deformed. Above this transition temperature, rock deforms in a ductile
or plastic manner, and there is no storage of elastic energy. Earthquakes therefore
indicate that the surrounding rock is at a sufficiently low temperature to
be able to store elastic energy.

Earthquakes are also diagnostic in that they reveal where deformation is actually
taking place. If there is no deformation, there is no accumulation of elastic
energy and hence none to be released in an earthquake. The general paucity
of earthquakes in plate interiors indicates that there is little deformation
occurring there. By contrast, the high density of earthquakes at plate boundaries
reveals that most of the deformation occurring across the earth’s surface
today is taking place precisely along these boundaries.

So what do the zones of intense seismicity which deepen with distance from
an ocean trench, i.e. the Wadati-Benioff zones, represent? From what we know
from rock physics, the high seismicity means that cooler rock is present and
also that this rock is undergoing active deformation. Is it not an entirely
reasonable inference that the cooler rock in which these earthquakes occur
is cool because it is part of a subducted oceanic lithosphere slab, especially
in view of the geometry of these zones? Laboratory experiments indicate that
deep-focus earthquakes, 300–700 km below the surface, occur by a somewhat
different mechanism than shallow earthquakes, but this mechanism also involves
rapid sliding on a fault plane in cold elastic rock as in the shallower events.5 I
am currently not aware of alternative explanations for the presence of cold,
actively deforming rock in such a special geometrical relationship to the ocean
trenches at depths up to 700 km, so I am eager to learn about them.

On the other hand, the GPS measurements, which now have such high precision
and such wide coverage, in concert with the earthquake data, which reveal so
precisely where and how the lithosphere is currently deforming, to me testify
in a convincing way the reality of active plate tectonics in our world today.

Black smokers and ridge topography testify to the reality of seafloor spreading

Additional evidence supporting this conclusion are the hot water vents, or ‘black
smokers’, observed along the mid-ocean ridges, as shown in Figure 4.6 Moreover,
the elevated topography of the ridges also indicates elevated temperatures
in the underlying rock column at the present moment, consistent with the spreading
process.7

Mega-earthquakes testify to the reality of subduction

Photo courtesy of TECFigure 5. GPS coseismic surface displacements of the 2011
Tohoku earthquake using 2-day site positions of 451 stations before and after
the main shock, the epicentre of which is marked by the star. Dashed line marks
trench location.

In addition, the mega-earthquakes occurring in the world today, including
the magnitude 9.0 Tohoku event off the coast of Honshu, Japan, in March 2011,
likewise testify to the present reality of plate motion and subduction.8 Figure
5 shows the displacement of the land surface in Honshu in response to the Tohoku
earthquake as documented by the change in location of 451 separate GPS stations.
This east-southeasterly motion represents elastic rebound of the body of rock
of which Honshu is a part that resulted from the slip and stress release on
the fault plane below. The elastic rebound of the downgoing plate presumably
was of similar amplitude but in the opposite direction. This means that the
downgoing plate in some places slipped, or subducted, some 8 m (26 ft) relative
to Honshu into the mantle beneath. With this portion of the fault locked for
more than a century, the westward motion of the Pacific Plate relative to Honshu
produced considerable accumulated elastic shortening in both plates. The presently
measured rate of 7.5 cm/yr implies 7.5 m of total shortening per century. Analysis
of the seismic waves generated by this event yielded a dip angle for the fault
plane of 14° to the west-northwest. The rectangular box in figure 5 encloses
the portion of the dipping fault plane over which most of the slip occurred.
The Global Seismographic Network, with more than 150 state-of-the-art digital
seismic stations, currently provides real-time open access data from which
details concerning the focal mechanism, the slip plane, the area and magnitude
of slip on the slip plane, and the earthquake magnitude can be determined.
Such analyses reveal, as in the case of the Tohoku event, the reality of subduction
in these contexts.

Volcanoes behind trenches confirm the reality of subduction

Photo courtesy of Smithsonian InstitutionFigure 6. Global distribution of volcanoes that have erupted
since 1964.

Additional evidence that points to the present reality of plate tectonics
is the current pattern of volcanic activity occurring across the face of the
earth. Figure 6 displays the locations of volcanoes that have erupted since
1964. The vast majority of these volcanoes are adjacent to deep ocean trenches
where active plate convergence is currently taking place. Many of the remainder
are on ocean islands, such as Iceland, Hawaii, Cape Verde, and Tristan da Cunha,
or in regions of continental extension such as East Africa. Why should there
be volcanism associated with plate convergence? The basaltic crust of the downgoing
slab generally contains a moderate amount of water in its pores and fractures
as well as within its hydrated minerals. As the slab descends to depths on
the order of 100–150 km, its basaltic crust encounters sufficient temperature
and pressure to cause this water to be released into the hot mantle rock above.9
Water, in turn, has the effect of lowering the melting temperature of this overlying
mantle rock sufficiently to initiate partial melting. The buoyant basalt magma
which this partial melting generates has a low viscosity and is usually able
to rise to the surface to produce volcanoes. The volcanism we observe today
so closely associated with the deep-ocean trenches, particularly along what
is known as the ‘Pacific Ring of Fire’, hence has a simple and
plausible explanation. As such, it represents another important complementary
strand of observational evidence that plate tectonics is indeed a truthful
description of the dynamics of the earth’s lithosphere in the present
day.

50–100 km of magma beneath mid-ocean ridges?

In his response to my letter in Journal of Creation 25(2),
Oard raises what he considers a problematic issue for plate tectonics. Somehow
he concludes that a 700°C higher average temperature in a 50–100
km rock column beneath a mid-ocean ridge, compared with such a column in the
lithosphere well away from the ridge, would require the column beneath the
ridge to be molten. I certainly never intended to give this impression.
Nothing in the professional literature suggests this even as a possibility.
Perhaps the sketch in figure 7 showing the relationship of a plate and the
asthenospheric mantle beneath as the plate migrates away from a ridge will
help clarify the issue. This trend of rapidly increasing lithospheric thickness
as a function of distance from a ridge is constrained by seafloor heat flow,
by seafloor topography, and by Love and Rayleigh seismic surface wave velocity
measurements.10 These datasets indicate
that oceanic plate thickness reaches a maximum value of about 90–100
km.10

Figure 7. Sketch showing slab of oceanic lithosphere bounded
by 0°C and 1100°C isotherms adjacent to a mid-ocean ridge. Passive
upwelling of solid peridotite mantle rock from the asthenosphere fills the
volume displaced by the slab as it moves to the right, relative to the ridge.
Peridotite is composed mostly of the minerals olivine and pyroxene. Partial
(up to 20%) melting of peridotite beneath the ridge produces basalt that rises
to the surface to form the ocean lithosphere crust, typically 5–7 km
thick.

The 1100°C isotherm is used here to define the base of the thermal lithosphere.
At temperatures of 1100°C and below, mantle rock displays considerable
strength to resist deformation, especially with warmer and much weaker asthenospheric
rock below it. A uniform vertical temperature gradient across the slab, consistent
with conductive cooling, implies an average slab temperature of about 550°C,
independent of its distance from the ridge.

The temperature, known as the solidus, at which the mineral with the lowest
melting temperature in a rock first begins to melt, is about 1200°C for
the peridotite mantle rock at shallow depths beneath a ridge.7 Solidus
temperature generally increases with increasing depth and pressure. With rock
solidus temperatures below a ridge in the range of 1200–1400°C, it
should be evident how the average temperature beneath a ridge can indeed be
700°C higher than within the corresponding depth range in the adjacent
oceanic lithosphere, and the rock still be mostly solid.

According to the best diagnostics available, this
is the way in which the basalt currently forming today’s new ocean crust
is being generated.

From an observational standpoint, the actual amount of melting that does occur
at mid-ocean ridges is tightly constrained by the observed thickness of the
oceanic crust, which is the uppermost portion of an oceanic lithospheric plate
as shown in figure 7. This crustal layer, typically 5–7 km thick, is
composed of basalt. Basalt is formed by partial melting of the peridotite mantle
rock. From the bulk chemistry differences between mid-ocean ridge basalt and
peridotite, laboratory studies constrain the melting fraction of the source
rock to be 20% or less.7 To generate 5–7
km of basalt therefore requires only 10–14% partial melting of a 50-km
thickness of mantle rock. Melting temperatures of silicate minerals, as mentioned
above, decrease with decreasing pressure or depth. As asthenospheric rock rises
passively beneath a ridge as the lithospheric plates move apart, some of the
minerals in the upward-moving rock which had been fully unmelted can suddenly
find themselves above their individual melting temperatures and begin to melt.
This process is commonly known as decompression melting. After only
a few percent partial melting, the molten fraction begins to mobilize, move
between mineral grains, and migrate toward the earth’s surface. According
to the best diagnostics available, this is the way in which the basalt currently
forming today’s new ocean crust is being generated.

Apparently, Oard’s failure to understand these aspects of mid-ocean
ridges allowed him to construct a straw man picture of 50–100 km of fully
molten rock beneath a ridge, a picture which he then used to ridicule
the process of seafloor spreading.

An appeal to move forward

In conclusion, given that the case that plate tectonics— as a present-day
reality—is supported by such compelling observational evidence, why should
this issue be a subject for debate in creation journals any longer? I find
it bewildering why Oard is opposed to the possibility that seafloor spreading
and subduction might actually be occurring even in the present day. In his
mind, just what in regard to creation science and the biblical account of earth
history is at risk? When one rejects uniformitarianism with its timescale,
just where do any remaining conflicts reside? On the other hand, as I have
stressed many times before, the plate tectonics picture, involving the earth’s
mantle as it does, seems to represent a gigantic breakthrough in understanding
earth history from a biblical standpoint. It provides the key to understanding
how a cataclysm as dramatic as the Genesis Flood, with the staggering tectonic
changes it brought to the earth, could unfold in a moderately orderly way and
in so brief an interval of time. With the current ferocity of the attacks on
the truthfulness of Genesis 1–11, how can we any longer afford to debate
an issue that is already fundamentally resolved? Is it not time to focus our
efforts earnestly toward applying the astonishing resources God has provided
to realize the defence of a young earth and a recent global Flood that His
honour deserves? Never before have such resources existed to accomplish this
task as are available today.

A detailed analysis of this earthquake performed by the Institute of Earth
Sciences, Acadamia Sinica, in Taiwan is available online at www.earth. sinica.edu.tw/~sjlee/eqks/20110311v2/index.htm. Return
to text.

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Readers’ comments

Mariusz K.,Poland, 31 August 2013

All these supposed evidence for plate tectonics are explained by Dr Brown's Hydroplate Theory, which in my opinion is far more plausible and compatible with the Bible than Plate Tectonics. Flood model based on Plate Tectonics is simply poor in my opinion.

Why would multiple points on a plate move in different directions? (i.e. radially in the Japanese map, and one point in photo--lower right-- showing opposing direction.) Would the Pacific trenches arcs and cusps similarities to collapsed hard shell of a ping pong ball offer some explanation of shattered crust settling rather than circulating?

Dr John Baumgardner responds

Note that Japan is not on the Pacific Plate. Neither is it on the Eurasian Plate. The velocities shown in Figure 2 are all horizontal velocities, so the velocity for the single station in Japan shown in Figure 2 is horizontal, not vertical. The other station you mention in the lower right part of Figure 2 likewise is not on the Pacific Plate. It is on the west side of the Tonga Trench in a region that is undergoing significant tectonic deformation. The Pacific Plate is subducting beneath this station. The motion of the Pacific Plate, as determined by these GPS measurements, implies ongoing subduction of the plate into the trenches along its western margin. Seismic imaging shows that the Pacific slab indeed is penetrating into the mantle at these locations.

Mark B.,Canada, 30 August 2013

Excellent points on both sides of the argument that clearly show that neither model works. This is a good case of creationism defeating creationism.

Mark

David S.,United States, 30 August 2013

10 years out of 6,000 is a small sample size but the GPS data is very precise. Has anyone attempted to fit a curve rather than a straight line to the GPS data?

Dr John Baumgardner responds

As far as I know, no one has attempted to fit the GPS data with anything other than straight lines, mainly because straight lines fit the data so well. Obvious exceptions are jumps in station locations that occur during nearby earthquakes. These jumps are marked by vertical red lines in the station motion history plots on the JPL/NASA website. Yes, ten years is short compared to 6,000 years, but it does seem long enough to obtain an amazingly precise estimate of the present plate motions. The current straight-line character in these datasets suggests that the earth has now largely stabilized since the tectonic convulsions it underwent during the Flood.

Jeff C.,United States, 30 August 2013

I find it strange that Darwinian Evolutionists can look at the evidence from observation in the real world today and claim a non-occurrence of a historical flood.

Many lines of observation show that catastrophic Floods Volcano's Earthquakes etc, have produced Canyons and other changes in the Earths landscape. Engineers Canyon produced by the eruption of Mt St Helens being one of the examples.

Daniel J.,United States, 30 August 2013

Peter, everytime skeptics like yourself mention the massive amounts of evidence supporting evolution and the age of the earth being billions of years old, I notice that you and them never mention any of this evidence. And in the rare occaions that you and other skeptics do mention evidence for evolution and the age of the earth being billions of years old, the 'evidence' always has a fatal crack in the 'logic' that's supposed to back it up.

Peter B.,Australia, 30 August 2013

I find it strange that you can accept the evidence for sea-floor spreading & continental drift but not that for the age of the Earth & the non-occurrence of the Genesis flood.

Tas Walker responds

Hi Peter, It is important to distinguish between evidence and interpretation. Creationists and evolutionists have the same evidence but come to different conclusions because of their different presuppositions. When we are considering what happened in the past, the same evidence can be interpreted in different ways. That is what a court trial is about—hearing evidence and argumentation for different positions about what happened in the past.